She's waiting for an apology. Katy Perry revealed during a Twitter Q&A on Saturday, September 10, that she'd collaborate with nemesis Taylor Swift on one condition: The "Bad Blood" singer has to say sorry.

While waiting in a "polka dot robe" for Cheesecake Factory to deliver her food, the "Rise" entertainer, 31, passed the time by having an impromptu chat with her Katy Kats.

However, things took a slightly awkward turn when one fan asked Perry if she'd be willing to record a song with Swift, who was once her close pal. "If she says sorry, sure!" the Grammy-nominated singer replied, sending tweeters into a frenzy.

Perry and Swift have had their fair share of ups and downs over the years. In July, the "Shake It Off" singer-songwriter's ex Calvin Harris slammed her in a lengthy Twitter rant in which he name-dropped Perry.

"I know you're off tour and you need someone new to try and bury like Katy ETC but I'm not that guy, sorry. I won't allow it," he wrote shortly after confirming that Swift wrote his Rihanna-featured summer hit "This Is What You Came For."

Perry seemingly threw shade at Swift shortly after, sharing a GIF of Hillary Clinton making an exasperated face before smiling and shrugging. The "Roar" songstress later retweeted one of her own tweets from May 2015 — "Time, the ultimate truth teller" — which she first shared when Swift called out an unnamed mean girl who allegedly betrayed her.

"For years, I was never sure if we were friends or not," the "Wildest Dreams" singer told Rolling Stone in September 2014. "She would come up to me at awards and say something and walk away, and I would think, Are we friends, or did she just give me the harshest insult of my life?"

Swift also explained that the conflict that ended the cryptic friendship was "so horrible. … She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me. … So now I have to avoid her. It's awkward, and I don't like it."